1. Field of the Invention
The invention is directed to an improved connection between a shaft end of a gas exchange valve of an internal combustion engine and a sleevelike actuating piston of a valve actuator.
2. Description of the Prior Art
One connection of the type with which this invention is concerned, known from German Patent Disclosure DE 198 26 046 A1, with at least two shell-like key pieces, which surround the shaft end and are axially braced on the actuating piston, whose radially outer circumferential surface extends conically, and which are surrounded by a conical fastening sleeve whose radially inner circumferential surface extends in complementary fashion to the cone angle of the key pieces, and which is axially braced against these key pieces by a nut screwed onto the shaft end. On the radially inner circumferential surface of the key pieces, there is an annular protrusion, which engages an annular groove on the radially outer circumferential surface of the shaft end. The actuating piston is formed by a differential piston, which depending on the pressure exerted on its piston faces, located on its face end and pointing away from one another, can slide up and down inside a cylindrical housing of the valve actuator. Because of the relatively high number of components that have to be assembled, however, the resultant production cost of this connection is high, and moreover the connection is relatively large.
Because according the invention the conical fastening sleeve is formed by the actuating piston, this actuating piston has a dual function; on the one hand, the hydraulic actuating forces engage it, and on the other, it assures the axial bracing of the conical connection, and hence a separate conical fastening sleeve can be dispensed with. Moreover, the threaded portions serving to brace the conical connection are embodied according to the invention on the actuating piston and on the key pieces, so that a lock nut can also be disposed with. The consequently reduced number of connection components makes assembly easier and faster; moreover, this reduces the amount of space the connection requires; and finally, the weight of the connection is also reduced.
In an especially preferred provision, on both the actuating piston and a key sleeve composed of the key pieces and extending all the way around, there is a respective engagement face for a screwing tool, which face is embodied in such a way that simultaneous engagement by connections associated with the engagement faces is possible. The key pieces and the actuating piston can then be screwed together in a single operation. Moreover, the connection is easily accessible from the outside, remote from the combustion chamber, through an opening in the valve actuator housing. Because the valve shaft need not project out of the opening for the sake of assembling the connection, it is possible in particular to use gas exchange valves with short shafts and hence with little mass inertia.
Another refinement provides that the connection is radially surrounded by the actuating piston, and a hydraulic region subjected to pressure fluid is disposed in a radially outer region of the actuating piston. The connection is not located in the pressure region, and so if the connection has to be loosened, for instance for repair purposes, the hydraulic circuit of the pressure region does not have to be opened.
Preferably, it is also provided that the key pieces viewed in the circumferential direction, adjoin one another seamlessly, i.e., without spacing, and together form a key sleeve extending all the way around, whose inside diameter is slightly greater than the outside diameter of the shaft end of the gas exchange valve, and that the protrusions and recesses engage one another with slight play. This creates a positive-engagement connection which has play and by means of which errors in concentricity between the valve seat and the guidance of the valve shaft can be compensated for. Moreover, rotary motions of the shaft end relative to the actuating piston are allowed. In that case, the known advantages of regular rotation of the gas exchange valve about its longitudinal axis, such as making valve wear uniform or keeping the valve seat free of deposits, can be attained without requiring that the actuating piston rotate along with the gas exchange valve, and thus the sealing function of the actuating piston is not impaired.
The actuating piston is preferably embodied in two parts and contains a closing piston near the combustion chamber and an opening piston remote from the combustion chamber, axially adjoining the closing piston and operating in the opposite direction from it, and the conical portion and the threaded portion are disposed on the opening piston.
In another embodiment, the actuating piston can also be embodied as a one-piece differential piston. In that case, the number of components is reduced further, and the length of the gas exchange valve can be even less, because the actuating piston can then be made comparatively shorter.